Answer:
(C) It provided a labor force for future oil and natural gas industries.
Explanation:
A:
It can't be A, because if miners and settlers had already made their industry in the Indian Territory, it wouldn't encourage miners to leave the area. Instead, the miners and settlers took control of the territory, and forced the Indians away.
B:
It can't be B, because the mining industry wasn't dependent on railroads; neither were railroads dependent on the mining industry.
D:
It can't be D, because the mining industry actually increased opportunities for small businesses!
